Inkjet printing is accomplished by ejecting ink from a nozzle toward paper or another print medium. The ink is driven from the nozzle toward the medium in a variety of ways. For example, in electrostatic printing, the ink is driven by an electrostatic field. Another ink jet printing procedure, known as squeeze tube, employs a piezoelectric element in the ink nozzle. Electrically-caused distortions of the piezoelectric element pump the ink through the nozzle and toward the print medium. In still another inkjet printing procedure, known as thermal or bubble inkjet printing, the ink is driven from the nozzle toward the print medium by the formation of an expanding vapor phase bubble in the nozzle. These various printing methods are described in “Output Hard Copy Devices,” edited by Durbeck and Sherr, Academic Press, 1988 (see particularly chapter 13, entitled “Ink Jet Printing”).
In addition to the generation of text print documents, inkjet printing and inkjet inks have become increasingly important in the generation of photographs created through digital means. This transformation has exposed a significant problem with current inkjet technology: many inkjet inks cannot attain a necessary degree of permanence to be used to record photographs. Unlike previous applications, photographs require long-term archivability. Instead of lasting for a few weeks or months, photographs are expected to remain unchanged for years or even decades.
The composition of an inkjet ink is traditionally comprised of deionized water, a water soluble organic solvent, and a colorant. The colorant may be a soluble dye or insoluble pigment. Dye based inks have been preferred for their brilliant color reproduction. However, many dye based inks can exhibit poor lightfastness, thermal stability, and/or oxidation characteristics. As a result, it can be impractical to use these dye based inks to record photographs. Evidence of an ink with poor lightfastness, poor thermal stability, and/or facile oxidation can be seen in an ink that fades over time.
Therefore, a need exists for dye based inks that can provide the appropriate color characteristics, such as hue and high chroma, and at the same time have an appropriate level of lightfastness or archivability.